Scores of French riot police descended early this morning on the "jungle" camp in Calais, bulldozing makeshift tents and rounding up hundreds of illegal migrants hoping to stow away on lorries to Britain.

A total of 278 people, nearly half of them minors, were detained as police moved into the camp shortly after dawn, dragging away camp dwellers and putting them into waiting buses. Those under 18 were to be transported to shelters in the east of France and adults to detention centres far from Calais.

The French immigration minister, Eric Besson, shrugged off criticism of the rough treatment of the migrants, most of whom are young Afghans in bureaucratic limbo, saying the jungle was a base for people-traffickers. "There are traffickers who make these poor people pay an extremely high price for a ticket to England," he said.

Police officers also clashed with protesters from the No Border movement, some of whom had come from England to demonstrate at the camp entrance against its destruction.

Last night, migrants were bracing for the police eviction, displaying banners demanding asylum rights. Adam Khan, 25, a former chauffeur from southern Afghanistan, said all he wanted to do was reach the UK.

"I've been here one month and I am trying and trying to go to England," he said. "The situation is bad in Afghanistan but I have relatives in England."

The fate of the detained migrants remains unclear. France is unlikely to return them forcibly to Afghanistan, and the most likely outcome is that they will be quickly released. Charities who provided food for the homeless migrants warned that the men were scared and distrustful, having witnessed brutality in police raids, and warned that many would end up sleeping rough again.

At its peak, the jungle was home to about 800 migrants, mostly Afghans, sleeping rough under scraps of sheeting. It had come to symbolise the failure of British and French authorities to deal with migrants desperate to reach the Kent coast but stuck in a no man's land.

Since the vast Red Cross centre at Sangatte was closed in 2002, under pressure from Britain, migrants have continued to gather along the coast desperate to reach the UK.

Sylvie Copyans, of the aid group Salam, said some of the migrants had been in the jungle camp for up to eight months.

"It's exactly like when they closed Sangatte," she said. "They are saying no immigrants in Calais, they can't stay here. But if they are made to leave they will just go to another squat. It's more and more difficult every day."

Activist group Refugee Action condemned the way the migrants had been treated. "They should never have been allowed to rot there like this. It's appalling neglect and has allowed false expectation to be built up," said Sandy Buchan, the group's chief executive.

But the home secretary, Alan Johnson, said he was delighted about the impending closure of the camp.

Britain has ruled out taking in the migrants. Johnson said genuine refugees should apply for asylum in the country where they entered the EU, while those not escaping persecution should return home.

Speaking after talks in Brussels with Besson yesterday, he said reports that Britain could be forced to take illegal immigrants were wrong.

"The measures that we have put in place are not only there to prevent illegal immigration but also to stop people-trafficking," Johnson said.

"We are working with the French, not only to strengthen our shared border but that of Europe as a whole."

Besson promised that more squats in the area would be gradually cleared. Migrants from Iraq, Afghanistan, Eritrea, Somalia and other countries have been living in squatted buildings and shacks all along the Nord-Pas-de-Calais coast, hoping to stow away on trucks heading to Britain.